Iodine and Starches: Learning Laboratory

The kids really enjoyed this simple experiment of using iodine to identify starch. I got to thinking about iodine after writing last week’s water post, because I remembered using iodine tablets to purify water when I went hiking on the Inca trail as a thirteen-year-old. It’s hard to visually explain that experiment, but the starch one is quite striking! I pulled out some iodine wipes (warning: iodine STAINS – be careful!), and we set up our experiment. Iodine in liquid form or tablet form can also be used; simply dissolve the tablets with a little bit of water for this experiment. I put flour, salt, and oatmeal on the plate, and then added baking powder on a whim, just to see what would happen.

Iodine and Starch Simple Experiment

Salt doesn’t have any starch, so the iodine stays brown.

Flour has a lot of starch! The iodine turned dark purple! We added a few drops of water with a syringe to help our drop of iodine to mix with the flour.

Oatmeal also has a lot of starch! It turned purple as well, although cooked oatmeal might have allowed the iodine to spread more thoroughly. Or a little more water =)

The baking soda bubbled up and turned purple at the edges. The purple is probably because most baking soda has some starch mixed in, but I’m still not sure why it bubbled. Does anyone know?

Update: It bubbles because baking powder contains baking soda – thanks to Carolyn Wilhelm and my IRL friend Kathy for reminding me of this! As Ann noted in her comment, baking soda reacts to acids, so the iodine must be slightly acidic. Here is Kathy’s explanation, if you would like the chemical details (thanks, Kathy!):

I think you created a chemical reaction with the Iodine (I2) baking soda NaHCO3 and water H20 to form a new chemical compound and also CO2 (gas) is a biproduct… which is what the bubbles would be… this is also what makes muffins, cookies, etc rise when baked is the release of the carbon dioxide gas…

The kids thought this was fascinating – and very strange! Johnny asked us to put it in the fridge for a while to see if that changed anything. It didn’t, but I was thrilled to see him taking our experiment one step further!

Funny, I accidentally did one part of your experiment when I was preparing our traditional gargle solution for Lars (he has a sore throat). Usually it’s soda, salt and iodine, but accidentally I put a baking powder instead. I didn’t see the bubbling, but my gargle turned purple. I was thinking of doing this experiment with Anna, since it’s very cool indeed.

I think Anna would really enjoy this experiment! Another commenter as well as one of my IRL friend reminded me that baking powder has baking soda in it (don’t know how I forgot that!) and that is probably why it is bubbling – the iodine must be slightly acidic? The bubbling was very slight, so you might not see it in a solution.

Very fun! There used to be a unit called mystery powders something like this. Doesn’t any liquid and baking soda cause bubbles? Learning like this is so wonderful for your children. Love the photos. Carokyn

I love experiments like this! Thanks for sharing at We Teach. My kids and I did an experiment with purple cabbage not too long ago. We soaked a coffee filter with boiled purple cabbage water, dried the filter, and used our filter to test ph levels. I’m sure you’d find the directions for experiments like this online. We’re going to try your experiment with iodine and some of the others you’ve shared. Thanks!

It was an amazing experience. We hiked a four-day segment in Bolivia, starting at 14,000 feet the first day, hiking up to 16,000 feet, and then down to 8,000 over the next three days. Parts of the trail were missing, but our guide knew their way. The first day was pretty grueling, but after that it was (literally) all downhill. Definitely something I’ll remember forever!